Andrey Litvinenko , Software Developer
Usually a data access object for MongoDB consists of common routine CRUD methods. Those methods should be
implemented, tested, maintained just like any other code. In this post, I'm going to show you how to use
SalatDAO to vastly simplify the process.
Generally, Salat is used for serialization of case classes,
enums and collections to
MongoDBObject (a key-value map which can be saved to the database) and back.
Salat uses Casbah library as an interface for
MongoDB. Also, Salat provides the
By extending this class, you can add a set of basic CRUD methods to your DAO. See these methods with comments
wiki might be helpful.
Let me demonstrate the suggested approach on the example of the DAO for the
Chocolate case class.
Here is the
Chocolate case class:
1 2 3 4 5 6
And here is the data access object for the
1 2 3 4 5 6 7
In order to extend
SalatDAO, you need to specify the case class type (
Chocolate), the id field type (
ObjectId) and initialize the MongoDB collection. In this example
"chocolate_base"is a MongoDB database name, and
"chocolate"- the collection name.
ChocolateDAO contains all the methods from the
BaseDAOMethods trait. However, many of those methods take
MongoDBObject as a parameter. It is a flaw in this approach: using these DAO methods makes your code database specific.
The easy and handy way to avoid this flaw is to use a case class with the implicit conversion instead of
Also, in order to build queries in an agile way, we will add a class that will be pretty similar to the
Chocolate case class,
but with a field type changed to
Option and a default value set to
None. That's how we will be able to search only by specific fields:
1 2 3 4 5 6
Here is an example of implicit conversions for the
Chocolate case class and
1 2 3 4 5 6 7 8 9 10 11 12 13
These conversions will help us to use case classes instead of
Now, you can use all the
SalatDAO methods in the much simpler way (see the example):
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
Basically, we've got CRUD methods for the DAO without implementing any of these methods. This approach will help you to avoid mistakes in the DAO code and save your time. Summarizing the flow, all you need to do is to:
- create a case class that represents your model
- add a similar case class (that will help to build queries) with a field type changed from
Option[X]and set a default value to
- create DAO class that extends
- implement implicit conversions to convert the created case classes into
All the sources are available on the GitHub repository.